The world depends on hydrocarbons to solve many of its energy needs. Consequently, oil field operators strive to produce and sell hydrocarbons as efficiently as possible. Much of the easily obtainable oil has already been produced, so new techniques are being developed to extract less accessible hydrocarbons. One such technique is steam-assisted gravity drainage (“SAGD”) as described in U.S. Pat. No. 6,257,334, “Steam-Assisted Gravity Drainage Heavy Oil Recovery Process”. SAGD uses pairs of vertically-spaced, horizontal wells less than about 10 meters apart.
In operation, the upper wells are used to inject steam into the formation. The steam heats the heavy oil, thereby increasing its mobility. The warm oil (and condensed steam) drains into the lower wells and flows to the surface. A throttling technique is used to keep the lower wells fully immersed in liquid, thereby “trapping” the steam in the formation. If the liquid level falls too low, the steam flows directly from an upper well to a lower well, reducing the heating efficiency and inhibiting production of the heavy oil. Such a direct flow (termed a “short circuit”) greatly reduces the pressure gradient that drives fluid into the lower wells.
Short circuit vulnerability can be reduced by carefully controlling the inter-well spacing. (Points where the inter-well spacing is too small will provide lower resistance to short circuit flows.) In the absence of precision drilling techniques, drillers are forced to employ larger inter-well spacings than would otherwise be desirable, so as to reduce the effects of inter-well spacing variances. Precision placement of neighboring wells is also important in other applications, such as collision avoidance, infill drilling, observation well placement, coal bed methane degasification, and wellbore intersections for well control.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the disclosed embodiments, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the appended claims.